The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A multi-speed transmission can use a combination of clutches, planetary gear arrangements, and fixed interconnections to achieve a plurality of gear ratios. In one example, friction type clutches are used in the transmission, and are selectively engaged to achieve a particular gear ratio. However, when disengaged, friction clutches tend to produce drag when there is relative motion between the clutch input member and the output member, which can lead to decreased fuel economy.
In an effort to improve fuel economy, a selectable one-way clutch (SOWC) may be employed instead of a friction clutch to transmit power from a first input member to a second driven member. Known SOWCs transmit torque in a first rotational direction and release or decouple in a second, opposite rotational direction. Once released, the driving member is free to rotate in the second opposite direction relative to the first direction, and the one-way clutch can overrun or freewheel. This allows the vehicle to travel in a coasting or gliding mode where the drivetrain is decoupled from the engine, thus minimizing losses associated with the drivetrain turning the engine.
Known SOWCs are commonly released at a near zero vehicle speed or when there is a positive input torque through the driveline. For example, the transmission may be precluded from proceeding with an upshift from a first gear to a second gear until the SOWC has released. To assist in controlling the transmission, known SOWC installations may include a release or position sensor to detect when the SOWC has been mechanically released. Drawbacks of the use of position sensors however, are that such sensors require their own installation space, power supply, and control system interface. In addition, certain transmission designs do not include position sensors that can be used for this purpose.
Thus, while current transmission SOWCs achieve their intended purpose, there is a need for a new and improved method for determining when a selectable one way clutch has mechanically released.